Suppressing nucleation and slow-kinetic epitaxial growth of large domain 2D nonlayered β-In₂S₃ nanoflakes via water molecules for optoelectronic devices

Abstract

Nonlayered two-dimensional (2D) β-In₂S₃ nanostructures have demonstrated outstanding electronic and optoelectronic properties, which requires its large-scale single-crystalline films to suppress carrier scattering. However, the weak energy for In−S chemical bonds and inherent nonlayered structure with three dimensional bonds make it highly challenging to achieve large area 2D β-In₂S₃ nanoflakes, which is still limited by the high nucleation density and three-dimensional isotropic growth tendency. Herein, we propose a universal strategy of suppressing nucleation and slow-kinetic epitaxial growth of large domain 2D nonlayered β-In₂S₃ nanoflakes via water molecules for the optoelectronic applications. The water molecules acted as the function of partially oxidized In₂S₃ nucleus via mild oxidation, which reduced the nucleation density by approximately three orders of magnitude and enabled the formation of large-area single-crystal with an average domain size of 120 μm and a maximum size approaching 270 μm. The structural characteristics and electronic structures of our β-In₂S₃ samples characterized by various characterization techniques showed unique single-crystalline nature and modified Fermi level properties. Furthermore, the diverse nanostructures of β-In₂S₃ could be precisely tuned from triangular nanosheets to nanowires by controlling the growth conditions. The two-terminal β-In₂S₃ photodetectors exhibited excellent performance with a high photoresponsivity of 44 A·W⁻¹ and a fast response speed with rise and decay times of 6 and 7 ms, respectively, revealing the superior physical properties of large domain 2D β-In₂S₃. This work provides a universal water-assisted strategy for synthesizing large-area 2D non-layered materials and paves the way for significant potential of high-quality large-scale single-crystalline β-In₂S₃ for advanced optoelectronic devices applications.

Graphical abstract

Keywords

two-dimensional nonlayered β-In₂S₃ / suppressing nucleation / slow-kinetic epitaxial growth / large domain size / optoelectronic devices

1 Introduction

As a new family of 2D materials, nonlayered ultrathin nano-flakes have been successfully synthesized even down to the monolayer limits, resolving isotropic growth problems due to three-dimensional crystal structures [1−14], which demonstrate unique physicochemical properties such as monolayer ferroelectricity and piezoelectricity, new types of magnetism, high optoelectronic performance [3, 8, 14−16]. Indium sulfide (In₂S₃), a representative of III−VI chalcogenides with diverse polymorphism, is an attractive n-type semiconductor with potential applications in solar cells and flexible optoelectronics [13, 17−20]. In₂S₃ compounds could crystallize as tetragonal β-In₂S₃, cubic α-In₂S₃, and trigonal layered γ-In₂S₃, which can be distinguished by different ordered indium vacancies [21]. Among these polymorphs, the tetragonal β-phase is most thermodynamically stable at room temperature. Meanwhile, 2D β-In₂S₃ have shown tunable defects related band gaps, high absorption coefficient, and excellent photoresponsivity, indicating the great potential for optoelectronic devices application [22, 23]. Therefore, optoelectronic device applications of 2D β-In₂S₃ nanoflakes request controllable synthesis of high-quality and large domain-sizes samples, which could largely reduce electronic scattering effects to improve optoelectronic devices performance [24].

Early research on the synthesis of 2D In₂S₃ primarily focused on the solution-phase methods, achieving polycrystalline 2D In₂S₃ with surface defects and contaminations [24, 25]. Subsequently, a space-confined chemical vapor deposition (CVD) was developed using InI₃ and sulfur powders, which demonstrated the synthesis of 2D In₂S₃ nanoflakes with lateral size of ~10 μm and lowest thickness of 1.5 nm with broadband response for high quantum efficiency [26]. However, CVD-synthesized In₂S₃ nanoflakes are generally limited in domain size, which largely limits its further application. Recently, physical vapor deposition (PVD) was applied to achieve a rapid growth of single crystal In₂S₃ with largest domain size of ~160 μm and a thickness of 20 nm, showing broadband response from visible to near-infrared region [22, 27]. However, conventional PVD synthesis of 2D β-In₂S₃ nanostructures with large domain sizes remains a significant challenge, suffering from inherent three-dimensional bonds, and relatively weak In−S bond strength induced high volatility of the In₂S₃ powder, often leading to excessively high nucleation density and resulting in the formation of polycrystalline film with limited domain size and poor thickness control [28-30]. Despite the above problems, recent progress still needs to pave a significant gap towards large-scale synthesis of single-crystalline 2D In₂S₃ film.

Here, we aim to address the nucleation and epitaxial growth issues by employing H₂O vapor to control the nucleation density and achieve large domain size of 2D β-In₂S₃ nanoflakes. This water-assisted PVD strategy greatly reduces the nucleation sites of 2D β-In₂S₃, which also results in ultrathin nanoflakes with lateral size of 270 μm with the thickness of 3.6 nm. The H₂O assisted growth mechanism is also revealed as the elemental step controls of suppressed nucleation and slow-kinetic epitaxy. The fabricated large domain 2D β-In₂S₃ photodetectors exhibit reasonable photo-response characteristics and a fast response speed.

2 Experimental section

2.1 Preparation of β-In₂S₃ nanoflakes

2D β-In₂S₃ nanoflakes were synthesized on mica substrate in an atmospheric pressure physical vapor deposition (APPVD) system using In₂S₃ powder as precursor. Specifically, 20−50 mg of In₂S₃ powder (99.9%, Macklin) was placed in the central zone of a quartz tube furnace. Two freshly cleaved mica substrates were positioned in the downstream low-temperature region, located 12−15 cm away from the In₂S₃ precursor. Before growth, the system was purged with high-purity argon (200 sccm) for approximately 10 minutes to remove residual air. The furnace temperature was then heated to 850  °C and the growth time was maintained for 10 min. During the growth process, the argon carrier gas (20−60 sccm) was directed through a glass bottle filled with deionized water to introduce a controlled amount of water vapor into the reaction environment to actively participate in the chemical vapor deposition process. After reaction completion, the system was allowed to cool naturally to room temperature under continuous argon flow of 20−60 sccm without water vapor, preserving the structural integrity of the as-grown samples.

2.2 Transfer of 2D β-In₂S₃ nanoflakes

The 2D β-In₂S₃ nanoflakes were transferred onto copper grid or SiO₂ using polymethyl methacrylate (PMMA)-assisted wet transfer process for TEM and Raman characterization. The In₂S₃/mica substrate was spin-coated with a 1 wt% PMMA solution: 10 s at 500 rpm for uniformity, followed by 50 s at 4500 rpm to achieve a thin and consistent film. The sample was then baked at 140 °C for 20 minutes to solidify the PMMA for its adhesion to In₂S₃ nanoflakes. And then the sample was immersed in a 1 wt% HF solution, enabling the PMMA/β-In₂S₃ film to detach from the mica substrate. The released film was immersed in deionized water to remove residual HF, then carefully transferred to the target substrate and baked at 90 °C for 5 minutes. Finally, the remaining PMMA was removed by immersing in hot acetone and isopropanol alcohol (about 70 °C), resulting in achieving clean β-In₂S₃ nanoflakes on the target substrates.

2.3 Characterization of 2D β-In₂S₃ nanoflakes

The optical microscope (OM, Olympus, BX53M) was used to obtain the surface morphology of our samples. The atomic force microscope (AFM, Oxford instruments, MPF-3D) equipped with scanning Kelvin Probe Force Microscopy (KPFM) was used to characterize micromorphology, thickness, and the surface potential of In₂S₃ nanowires or nanoflakes. The Raman spectrometer (Raman, Thermo Fisher Scientific, DXR3) with 532 nm laser as the excitation wavelength was used to characterize the phase of In₂S₃ samples. The transmission electron microscopy (TEM, FEI Tecnai F20) equipped with an energy dispersive X-ray (EDX) spectrometer was used to analyze the crystal structure and elemental composition of β-In₂S₃ nanoflakes, while selected-area electron diffraction data were also collected by the SAED module.

2.4 Fabrication and measurements of 2D β-In₂S₃ photodetectors

The device is fabricated via an Ultraviolet Maskless Lithography machine (TuoTuo Technology (Suzhou) Co., Ltd.). The electrodes were patterned on the β-In₂S₃ nanoflakes on mica substrates, and then metal films of In/Au (10/50 nm) were deposited by thermally evaporated deposition device (VNANO, VZZ-300S). The electrical and optoelectrical properties of β-In₂S₃ were characterized at room temperature using semiconductor analyzer system (PDA, FS-Pro) equipped with a probe station. The photodetector was illuminated with laser diodes at wavelengths of 520 nm and 650 nm and the incident optical power was measured using an optical power meter (Newport 843-R) to ensure reliable illumination conditions.

3 Results and discussion

Figure 1(a) shows the schematic of water-assisted growth strategy on mica substrate, in which high-purity In₂S₃ (~99.9%) powder was placed in the central zone of tube furnace. Two cleaved mica substrates were positioned at ~13−15 cm downstream from the In₂S₃ powder. High-purity argon (Ar) flow was introduced through a glass bottle containing deionized water, where the evaporated In and S clusters can mix with Ar-H₂O vapor, thereby participating in the nucleation and epitaxy processes (Fig. S1 of the Electronic Supplementary Materials). The Ar flow rate is directly proportional to the number of H₂O molecules, achieving the appropriate amount for tuning reaction kinetics. At room temperature, β-In₂S₃ has the covalent bonded nonlayered tetragonal structure, which belongs to the I4₁/amd space group with lattice constants of a = b = 7.68 Å, c = 32.62 Å, and α = β = γ = 90° [Figs. 1(b) and S2] [21]. The atomic structure of (10\overline{6}) plane shows tetragonal symmetry with ordered vacancies, while the (103) plane belongs quasi-triple symmetric structure. Optical image (OM) of 2D In₂S₃ nanoflakes obtained under Ar-H₂O flow rate of 20 sccm is shown in Fig. 1(c), exhibiting nucleation density is two orders of magnitude lower than that of the samples grown without H₂O (detailed in Fig. S3). The pyramid domain morphology of In₂S₃ nanoflakes [Fig. 1(c)] indicates water molecules actively influence the reaction kinetics, promoting a quasi-layer-by-layer growth mechanism. Large domain size of ~270 μm 2D In₂S₃ nanoflakes [Fig. 1(d)] were obtained by optimizing growth parameters, which strongly confirms that the participation of H₂O facilitates larger In₂S₃ domains. Atomic force microscopy (AFM) characterization reveals the thickness can be controlled from 3.5 nm to 14.4 nm [Figs. 1(e) and S4], exhibiting uniform surface and high crystalline quality. Therefore, water molecules play an important role in suppressing nucleation and promoting lateral expansion of domains.

Raman spectrum of the water-assisted In₂S₃ exhibits four distinct peaks at 247, 309, 323, and 367 cm⁻¹ [Fig. 1(f)]. The peaks at 247 cm⁻¹ and 367 cm⁻¹ can be assigned to A_1g vibrational modes of β-In₂S₃, while the Raman peaks at 309 cm⁻¹ and 323 cm⁻¹ correspond to E_g modes of β-In₂S₃ [22, 31, 32]. Meanwhile, thickness dependent Raman measurements were also conducted to characterize 2D β-In₂S₃ [Fig. 1(g)]. For ultrathin samples below 10 nm, only two characteristic peaks of A_1g (247 cm⁻¹) and A_1g (367 cm⁻¹) were observed, whereas the E_g vibrational mode at 309 and 323 cm⁻¹ were suppressed. As the thickness increased, the peak around 315 cm⁻¹ split into two distinct peaks, identified as the E_g (309 cm⁻¹) and E_g (321 cm⁻¹). To evaluate the structural stability of β-In₂S₃, we compared the Raman spectra of sample exposed to ambient and stored under vacuum for six months (Fig. S5). The spectrum of β-In₂S₃ exposed to ambient air shows an additional prominent peak emerges at around 130 cm⁻¹, which matches the characteristic Raman mode of In₂O₃ [33]. In contrast, the Raman spectrum of vacuum-stored sample does not exhibit noticeable peak shift. These results indicate that β‑In₂S₃ maintains its structural stability when kept in a vacuum environment. Figure 1(h) presents X-ray photoelectron spectroscopy (XPS) analysis of the as-grown sample before and after six months of exposure to ambient air. For the freshly synthesized sample, the In 3d core-level spectrum exhibits two obvious peaks of 444.7 eV and 452.2 eV, corresponding to the In 3d_5/2 and In 3d_3/2, respectively, which shows the energy splitting (ΔE) of 7.5 eV in agreement with previously reported β-In₂S₃ [32, 34]. In addition, after air exposure for six months, the XPS spectrum exhibits two distinct peaks at 446.2 and 453.7 eV, indicating surface oxidation after long time air exposure leads to the weak formation of In−O bonds and its reasonable stability [34, 35]. Therefore, the water-assisted grown In₂S₃ samples are clearly identified as the β-phase and exhibit high purity and excellent crystalline quality. Moreover, XPS spectra for In 3d reveal a higher binding energy for the water assisted grown In₂S₃ nanoflakes compared to the sample stored for 6 months, indicating a potential modified surface environment with trace In−O bonding. This shift aligns with the higher electronegativity of oxygen relative to sulfur.

Transmission electron microscopy (TEM) and selected-area electron diffraction (SAED) were employed to characterize crystalline microstructure and chemical composition of β-In₂S₃ samples, which were transferred onto copper grids using wet chemical etching method [8]. High-resolution TEM (HRTEM) image revealed the clear lattice fringe of 3.9 Å, which was indexed as the distance of (020) plane for β-In₂S₃ [Fig. 2(a)]. The corresponding SAED pattern [Fig. 2(b)] displays a hexagonal symmetric diffraction spot, matching well with the simulated diffraction along the [601] zone axis [Fig. 2(c)] and confirming single crystalline structure with quasi-triple symmetry. The elemental energy-dispersive X-ray spectroscopy (EDS) maps of In and S elements showed uniform distribution of In and S elements across the In₂S₃ nanoflake [Figs. 2(e) and (f)], respectively, which correspond to the area outlined in low-magnification TEM image [Fig. 2(d)]. The analysis of the EDS spectrum yields an atomic ratio of In to S approximately 39.7:60.3 (Fig. S6), which further confirms the high chemical purity and correct stoichiometry of our samples. The SAED pattern is indexed to the [601] zone axis, which is perpendicular to the (020) plane. By understanding theoretical atomic structure of β-In₂S₃ [Fig. 2(g)], the crystallographic orientation relative to the substrate can be unambiguously determined, finally revealing the horizontal growth plane corresponds to the (103) crystal plane.

Figure 3(a) shows the proposed schematic of water-assisted growth mechanism. As supported by prior studies, H₂O molecules can act as a mildly partial oxidizing agent at high temperature [36]. Herein, we propose that the introduction of H₂O molecules can oxidize partial In−S clusters, inhibiting their function as active epitaxial growth centers and thereby dramatically reducing the overall nucleation density. The precursor flux is concentrated on the limited number of nucleus active sites, promoting lateral expansion via a slow kinetic process and enabling the formation of large-domain 2D β-In₂S₃ nanoflakes. The XPS results confirm that the mild oxidizing property of H₂O molecules does not completely oxidize In−S bonds into In−O bonds during the epitaxy process [37]. Therefore, H₂O molecules act as the passivators that prevent large number of In−S clusters becoming epitaxial centers during the nucleation stage, which largely reduces nucleation densities and expands the domain size.

To elucidate the water-assisted growth mechanism, a series experiments were conducted to investigate the influence of critical parameters. The morphological evolution of 2D β-In₂S₃ was achieved by controlling Ar flow rate to modulate the growth kinetics in different atmospheres with and without H₂O (Figs. 3 and S7). The optical images of β-In₂S₃ grown with H₂O at Ar flow rates from 20 to 60 sccm at 600 °C are shown in Figs. 3(b)−(d). As the effective supply of H₂O molecules enhanced, the average lateral domain size expanded from approximately 5 μm to 80 μm. Meanwhile, the estimated nucleation densities decreased from 7.1 × 10⁸ m⁻² to 3.3 × 10⁷ m⁻² [Fig. 3(e)]. In contrast, we evaluated the results of 2D β-In₂S₃ grown in pure Ar gas under identical growth conditions. Although the nucleation density experienced a slight decrease from 7.7 × 10¹¹ m⁻² to 2.2 × 10¹⁰ m⁻² with increased flow rate, it remains at a relatively higher order of magnitude [Figs. 3(f)−(h)], also showing the restricted domain size of ~20 μm. Further epitaxial growth results in the formation of polycrystalline films with diverse grain boundaries and defects. To further check the general influence of H₂O molecules, we conducted similar experiments on C-sapphire substrates. AFM image of β-In₂S₃ (Fig. S8) grown without H₂O showed high nucleation density with domain sizes of ~500 nm. When H₂O molecules were introduced into the atmosphere, the average domain size increased to 4−6 μm. These findings confirm that the general applicability of water-assisted strategy of synthesizing large-domain 2D β-In₂S₃ on diverse substrates.

The optical images of In₂S₃ samples grown at the temperature of 500 °C, 550 °C, and 600 °C for 10 minutes were shown in Figs. 4(a)−(c), respectively. At 600 °C, the β-In₂S₃ exhibits regular triangular crystalline domain [Fig. 4(a)]. When the temperature decreased to 550 °C, one-dimensional nanowire structures coexisted with the nanoflake morphology [Fig. 4(b)]. As the growth temperature further reduced to 500 °C, the dominant morphology of samples shifted to nanowires [Fig. 4(c)]. The grown results within the temperature range of 550−600 °C are presented in Fig. S9, exhibiting a more clearly transition process. This morphological evolution may be attributed to modified kinetic control at lower temperatures, which promotes the rapid deposition of In₂S₃ on specific crystal planes. At the high temperature, In−S atoms or clusters on the substrate possess higher mobility. Therefore, the growth process is thermodynamically driven towards the formation of 2D nanoflakes, which represent the structure with lowest surface energy for the crystal orientation [3]. Conversely, at the low temperature, the diffusion ability of atoms or clusters is significantly limited, thus hindering the formation of 2D structure. Instead, atoms preferentially migrate to dangling bonds or defect sites on nanowires, leading to the deposition of specific crystal direction [38−41]. Figure 4(d) shows Raman spectrum of In₂S₃ nanowires on the SiO₂ substrate. Three distinct characteristic peaks are observed at A_1g (247 cm⁻¹), E_g (309 cm⁻¹), and A_1g (367 cm⁻¹), which are identical to β-In₂S₃ nanoflakes [Fig. 1(f)]. With the growth temperature fixed at 500 °C, the influence of Ar flow rate (with H₂O) on the nanowire growth was examined. As the flow rate increased from 20 to 60 sccm, the nucleation densities of β-In₂S₃ nanowires dramatically decreased by 1−2 orders of magnitude, while the maximum length of nanowires increased to ~100 μm [Figs. 4(e)−(g)]. This finding further confirms the nucleation suppression by H₂O molecules, which is consistent with our observations in the In₂S₃ nanoflake (Fig. 3). As depicted in Fig. 4(h), the AFM image and corresponding height profile of the In₂S₃ nanowire reveal a uniform nanowire morphology with a thickness of ~60 nm (Fig. S10), demonstrating well-defined structural integrity.

To investigate the optoelectronic properties of large domain 2D β-In₂S₃ nanoflakes grown with H₂O, roomtemperature electrical transport measurements were carried out. We constructed two-terminal β-In₂S₃ photodetectors on mica substrate, the schematic device configuration of which is shown in Fig. 5(a). The electrodes were patterned via direct-writing ultraviolet lithography equipment, followed by the deposition of 10 nm In and 50 nm Au layers as contact electrodes. The channel length was controlled to be ~6 μm. Figure 5(b) shows the differences of surface potential between In₂S₃ grown with H₂O and without H₂O, as measured by Au-referenced scanning Kelvin Probe Force Microscopy (KPFM). The results indicate that the work function of β-In₂S₃ nanoflakes grown with H₂O is 0.08 eV lower than that of β-In₂S₃ nanoflakes grown without H₂O, confirming a shift of the Fermi level toward a more intrinsic position [Figs. S11 and S12]. The surface potential mappings [Fig. 5(b)] suggest the different surface environments between two sample types. The current voltage (I−V) characteristics of β-In₂S₃ photodetector were measured under 650 nm laser illumination with different optical powers. The I−V curves demonstrate obvious rectification behavior within the voltage range of −2.5 V to 2.5 V [Fig. 5(c)], suggesting the Schottky contact at the semiconductor-electrode interface [42]. When the incident power increased from dark states to 0.67 nW, the photocurrent (V_ds = 2.5 V) increased from 1.5 nA to 25.7 nA. The R_{\lambda } increases nearly linearly with the increasing optical power [Fig. 5(d)], reaching a maximum R_{\lambda } of 44 A·W⁻¹ at an incident power of 0.07 nW and a bias voltage of 2 V [43].

The temporal photocurrent of the device was evaluated under 520 nm illumination at a bias of 1 V. Figure 5(e) shows the time-resolved photocurrent curve of the β-In₂S₃ photodetector measured at different power densities. As the light power density increased from 59 mW·cm⁻² to 147 mW·cm⁻², the photocurrent rose from about 0.1 nA to 0.25 nA, demonstrating a clear positive correlation with high photosensitivity. However, when the power density further increased to 232 mW·cm⁻², a reduction in the photocurrent is observed. This reduction can be attributed to the rapid saturation of trap states under strong illumination, which may limit efficient carrier generation and result in a lower photocurrent. All measured photocurrent curves exhibit stable, uniform, and highly reproducible switching characteristics over multiple cycles, demonstrating the robust and reliable photo-response stability of the β-In₂S₃ device. Figure 5(f) shows the response speed of the β-In₂S₃ device under 520 nm illumination, where the rise time ({\tau }_{\mathrm{r}\mathrm{i}\mathrm{s}\mathrm{e}}) and decay time ({\tau }_{\mathrm{d}\mathrm{e}\mathrm{c}\mathrm{a}\mathrm{y}}) are estimated to be ~ 6 ms and 7 ms, respectively. Compared to previous reports, our β-In₂S₃ sample exhibits a faster response time and excellent performance (Table S1). The energy band diagram under different states were schematically presented in Figs. 5(g)−(i). Figure 5(g) shows the band structure of the metal electrode prior to contact with the semiconductor. The Fermi level of β-In₂S₃ is approximately 4.75 eV, which is slightly higher than the work function of the In electrode (4.1 eV), inducing downward band bending at the interface and leading to the Schottky barrier [Fig. 5(h)]. The unequal contact areas of source and drain electrodes result in the formation of unbalanced charge injection effects [Fig. 5(b)], which contributes to final rectification characteristics. Under external bias and light illumination, photogenerated electron−hole pairs are driven in opposite directions across the Schottky barrier, thereby generating photocurrent under the bias [Fig. 5(i)]. In addition, the abundant trap states allow the capture of the photogenerated excitons by defect-related energy levels, resulting in prolonged carrier lifetimes and enhanced photo-response performance. Therefore, this work provides the mechanism understanding of 2D β-In₂S₃ photodetectors and the potential for large-scale integration in optoelectronic applications [44, 45].

4 Conclusion

In this study, high-quality 2D single-crystal β-In₂S₃ nanoflakes were synthesized via water-assisted PVD strategy. The mild oxidation of H₂O vapor effectively passivates In−S clusters, thereby inhibiting the nucleation density of In₂S₃ by three orders of magnitude and enabling the formation of large-area single crystals with a maximum size approaching 270 μm. Photodetectors based on water-assisted grown β-In₂S₃ exhibited excellent performance, including a high photoresponsivity of 44 A·W⁻¹ and a fast response speed with rise and decay times of 6 and 7 ms, respectively. In conclusion, this work provides a new strategy for synthesizing large domain 2D non-layered materials for advanced optoelectronic devices applications.

References

[1] K. Chang , J. Liu , H. Lin , N. Wang , K. Zhao , A. Zhang , F. Jin , Y. Zhong , X. Hu , W. Duan , Q. Zhang , L. Fu , Q. K. Xue , X. Chen , and S. H. Ji , Discovery of robust in-plane ferroelectricity in atomic-thick SnTe, Science 353(6296), 274 (2016)

[2] Y. Wu , J. Zheng , Q. Li , M. Song , S. Yue , N. Lin , and L. Jiao , Synthesis of superconducting two-dimensional non-layered PdTe by interfacial reactions, Nat. Synth. 1(11), 908 (2022)

[3] B. Li , Z. Wan , C. Wang , P. Chen , B. Huang , X. Cheng , Q. Qian , J. Li , Z. Zhang , G. Sun , B. Zhao , H. Ma , R. Wu , Z. Wei , Y. Liu , L. Liao , Y. Ye , Y. Huang , X. Xu , X. Duan , W. Ji , and X. Duan , Van der Waals epitaxial growth of air-stable CrSe₂ nanosheets with thickness-tunable magnetic order, Nat. Mater. 20(6), 818 (2021)

[4] X. Guo , X. Zhou , W. Chu , X. Fan , C. Li , L. Zou , C. Niu , B. Zhang , Y. Lu , H. Zhang , F. OuYang , Z. Wu , and Y. Zhou , Remote vapor-phase dual alkali halide salts assisted quasi-van der Waals epitaxy of m-phase ZrO₂ thin films with high dielectric constant and stable flexible properties, Appl. Phys. Lett. 125(8), 084101 (2024)

[5] X. Fan , L. Zou , W. Chu , L. Wang , and Y. Zhou , Synthesis of high resistive two-dimensional nonlayered Cr₂S₃ nanoflakes with stable phosphorus dopants by chemical vapor deposition, Appl. Phys. Lett. 122(22), 222101 (2023)

[6] X. Fan,J. Yi,B. Deng,C. Zhou,Z. Zhang,J. Yu,W. Li,C. Li,G. Wu,X. Zhou,T. Sun,Y. Zhu,J. Zhou,J. Xia,Z. Wang,K. Lai,Z. Peng,D. Li,A. Pan,Y. Zhou, 2D edge-seeded heteroepitaxy of ultrathin high-κ dielectric CaNb₂O₆ for 2D field-effect transistors, Nat. Commun. 16(1), 2586 (2025)

[7] W. Chu , R. Xin , L. Zou , X. Fan , X. Zhou , C. Li , and Y. Zhou , Synthesis of nonlayered 2D α-Fe₂O₃ nanosheets by ultralow concentration precursor with Se catalysts design, Phys. Status Solidi RRL. 18(7), 2300102 (2023)

[8] H. Chen , Z. Tian , X. Zhou , X. Fan , Z. Li , C. Li , C. Niu , W. Chu , Y. Zhou , L. He , Y. Yang , Z. Peng , and Y. Zhou , Approaching charge compensation limit for promoting magnetoresistance in 2D nonlayered MoO₂ via surface hydrogen passivation, Adv. Funct. Mater. 35(22), 242204 (2025)

[9] J. Shen , Y. Xie , and J. J. Cha , Revealing surface states in In-doped SnTe nanoplates with low bulk mobility, Nano Lett. 15(6), 3827 (2015)

[10] J. Shen , Y. Jung , A. S. Disa , F. J. Walker , C. H. Ahn , and J. J. Cha , Synthesis of SnTe nanoplates with {100} and {111} surfaces, Nano Lett. 14(7), 4183 (2014)

[11] N. Syed , A. Zavabeti , K. A. Messalea , E. Della Gaspera , A. Elbourne , A. Jannat , M. Mohiuddin , B. Y. Zhang , G. Zheng , L. Wang , S. P. Russo , D. Esrafilzadeh , C. F. McConville , K. Kalantar-Zadeh , and T. Daeneke , Wafer-sized ultrathin gallium and indium nitride nanosheets through the ammonolysis of liquid metal derived oxides, J. Am. Chem. Soc. 141(1), 104 (2019)

[12] Y. Chen , K. Liu , J. Liu , T. Lv , B. Wei , T. Zhang , M. Zeng , Z. Wang , and L. Fu , Growth of 2D GaN single crystals on liquid metals, J. Am. Chem. Soc. 140(48), 16392 (2018)

[13] F. Horani and E. Lifshitz , Unraveling the growth mechanism forming stable γ-In₂S₃ and β-In₂S₃ colloidal nanoplatelets, Chem. Mater. 31(5), 1784 (2019)

[14] C. Gong , J. Chu , C. Yin , C. Yan , X. Hu , S. Qian , Y. Hu , K. Hu , J. Huang , H. Wang , Y. Wang , P. Wangyang , T. Lei , L. Dai , C. Wu , B. Chen , C. Li , M. Liao , T. Zhai , and J. Xiong , Self‐confined growth of ultrathin 2D nonlayered wide‐bandgap semiconductor CuBr flakes, Adv. Mater. 31(36), 1903580 (2019)

[15] C. Chang , W. Chen , Y. Chen , Y. Chen , Y. Chen , F. Ding , C. Fan , H. Jin Fan , Z. Fan , C. Gong , Y. Gong , Q. He , X. Hong , S. Hu , W. Hu , W. Huang , Y. Huang , W. Ji , D. Li , L. J. Li , Q. Li , L. Lin , C. Ling , M. Liu , N. Liu , Z. Liu , K. Ping Loh , J. Ma , F. Miao , H. Peng , M. Shao , L. Song , S. Su , S. Sun , C. Tan , Z. Tang , D. Wang , H. Wang , J. Wang , X. Wang , X. Wang , A. T. S. Wee , Z. Wei , Y. Wu , Z. S. Wu , J. Xiong , Q. Xiong , W. Xu , P. Yin , H. Zeng , Z. Zeng , T. Zhai , H. Zhang , H. Zhang , Q. Zhang , T. Zhang , X. Zhang , L. D. Zhao , M. Zhao , W. Zhao , Y. Zhao , K. G. Zhou , X. Zhou , Y. Zhou , H. Zhu , H. Zhang , and Z. Liu , Recent progress on two-dimensional materials, Acta Phys. Chim. Sin. 37(12), 2108017 (2021)

[16] B. Jin , P. Huang , Q. Zhang , X. Zhou , X. Zhang , L. Li , J. Su , H. Li , and T. Zhai , Self‐limited epitaxial growth of ultrathin nonlayered CdS flakes for high‐performance photodetectors, Adv. Funct. Mater. 28(20), 1800181 (2018)

[17] W. Chu , X. Zhou , Z. Wang , X. Fan , X. Guo , C. Li , J. Yue , F. Ouyang , J. Zhao , and Y. Zhou , Stable alkali halide vapor assisted chemical vapor deposition of 2D HfSe₂ templates and controllable oxidation of its heterostructures, Front. Phys. (Beijing) 19(3), 33212 (2024)

[18] X. Fan , R. Xin , L. Li , B. Zhang , C. Li , X. Zhou , H. Chen , H. Zhang , F. OuYang , and Y. Zhou , Progress in the preparation and physical properties of two-dimensional Cr-based chalcogenide materials and heterojunctions, Front. Phys. (Beijing) 19(2), 23401 (2024)

[19] P. Wang,W. Xue,J. Zeng,W. Ci,Q. Chen,B. Lv,R. Yang,Y. Liu,G. Liu,X. Xu, Wavelength-selective photodetector and neuromorphic visual sensor utilizing intrinsic defect semiconductor, Adv. Funct. Mater. 34(46), 2407746 (2024)

[20] Y. Zhou , D. Wu , Y. Zhu , Y. Cho , Q. He , X. Yang , K. Herrera , Z. Chu , Y. Han , M. C. Downer , H. Peng , and K. Lai , Out-of-plane piezoelectricity and ferroelectricity in layered α-In₂Se₃ nanoflakes, Nano Lett. 17(9), 5508 (2017)

[21] P. Pistor , J. M. Merino Álvarez , M. León , M. di Michiel , S. Schorr , R. Klenk , and S. Lehmann , Structure reinvestigation of α-, β- and γ-In₂S₃, Acta Crystallogr. B 72(3), 410 (2016)

[22] Y. Zhao , D. Yu , J. Lu , L. Tao , Z. Chen , Y. Yang , A. Wei , L. Tao , J. Liu , Z. Zheng , M. Hao , and J. B. Xu , Thickness‐dependent optical properties and In‐plane anisotropic Raman response of the 2D β‐In₂S₃, Adv. Opt. Mater. 7(22), 1901085 (2019)

[23] J. Zhu , S. Wu , L. Wang , J. Wu , J. Zhu , L. Zou , F. Xiao , Z. Su , C. Jiao , S. Pei , Z. Zhang , J. Qin , B. Xu , Y. Zhou , J. Xia , and Z. Wang , Broad‐range, high‐linearity, and fast‐response pressure sensing enabled by nanomechanical resonators based on 2D non‐layered material: β-In₂S₃, InfoMat 6(8), e12553 (2024)

[24] S. Sarkar , A. D. P. Leach , and J. E. Macdonald , Folded nanosheets: A new mechanism for nanodisk formation, Chem. Mater. 28(12), 4324 (2016)

[25] W. Wang , Z. Chen , X. Sui , Y. Li , X. Liu , Y. Zhang , Phase/size dual controlled 2D semiconductor In₂X₃ (X = S , and Se , Te) for saturable absorption modulation, Nano Res. 15(6), 5633 (2022)

[26] C. L. Tu,K. I. Lin,J. Pu,T. F. Chung,C. N. Hsiao,A. C. Huang,J. R. Yang,T. Takenobu,C. H. Chen, CVD growth of large-area InS atomic layers and device applications, Nanoscale 12(17), 9366 (2020)

[27] J. Lu , Z. Zheng , W. Gao , J. Yao , Y. Zhao , Y. Xiao , B. Wang , and J. Li , Epitaxial growth of large-scale In₂S₃ nanoflakes and the construction of a high performance In₂S₃/Si photodetector, J. Mater. Chem. C 7(39), 12104 (2019)

[28] N. Kaur , D. Sharma , B. R. Mehta , Growth of In₂S₃ nanolayers on F-Mica , and SiO₂ , ZnO, and TiO₂ substrates using chemical vapor deposition, Mater. Sci. Eng. B 264, 114889 (2021)

[29] D. Yu , Z. Zhuo , A. Wei , J. Liu , Y. Zhao , and Z. Xiao , Growth of large-area two-dimensional non-layered β-In₂S₃ continuous thin films and application for photodetector device, J. Mater. Sci. Mater. Electron. 31(20), 18175 (2020)

[30] K. Zhang , Y. She , X. Cai , M. Zhao , Z. Liu , C. Ding , L. Zhang , W. Zhou , J. Ma , H. Liu , L. J. Li , Z. Luo , and S. Huang , Epitaxial substitution of metal iodides for low-temperature growth of two-dimensional metal chalcogenides, Nat. Nanotechnol. 18(5), 448 (2023)

[31] Y. Chen , Z. Huang , Y. You , T. Jiang , H. Wu , Z. Zheng , C. Du , K. Chen , and T. Lai , Thickness-dependent optical properties and ultrafast carrier dynamics of 2D non-layered β-In₂S₃, APL Mater. 13(2), 021105 (2025)

[32] W. Huang , L. Gan , H. Yang , N. Zhou , R. Wang , W. Wu , H. Li , Y. Ma , H. Zeng , and T. Zhai , Controlled synthesis of ultrathin 2D β‐In₂S₃ with broadband photoresponse by chemical vapor deposition, Adv. Funct. Mater. 27(36), 1702448 (2017)

[33] N. Zhao , X. Chang , X. Liu , J. Li , W. Zheng , and J. Zhang , Probing the structural dynamics of In₂O₃ using in situ raman spectroscopy: Bridging material dynamics and sensor functionality, Angew. Chem. Int. Ed. 64(45), e202512808 (2025)

[34] K. Wang , Y. Hu , X. Liu , J. Li , and B. Liu , Visible-light-driven CO₂ photoreduction over atomically strained indium sites in ambient air, Nat. Commun. 16(1), 2094 (2025)

[35] A. Kyndiah,A. Ablat,S. Guyot-Reeb,T. Schultz,F. Zu,N. Koch,P. Amsalem,S. Chiodini,T. Yilmaz Alic,Y. Topal,M. Kus,L. Hirsch,S. Fasquel,M. Abbas, A multifunctional interlayer for solution processed high performance indium oxide transistors, Sci. Rep. 8(1), 10946 (2018)

[36] P. Li and J. Zhang , Sorting out semiconducting single-walled carbon nanotube arrays by preferential destruction of metallic tubes using water, J. Mater. Chem. 21(32), 11815 (2011)

[37] A. Cohen , A. Patsha , P. K. Mohapatra , M. Kazes , K. Ranganathan , L. Houben , D. Oron , and A. Ismach , Growth-etch metal–organic chemical vapor deposition approach of WS₂ atomic layers, ACS Nano 15(1), 526 (2021)

[38] Q. Su , C. K. Huang , Y. Wang , Y. C. Fan , B. A. Lu , W. Lan , Y. Y. Wang , and X. Q. Liu , Formation of vanadium oxides with various morphologies by chemical vapor deposition, J. Alloys Compd. 475(1−2), 518 (2009)

[39] Q. Su,X. Pan,E. Xie,Y. Wang,J. Qiu,X. Liu, Influence of temperature on the microstructure of V₂O₅ film prepared by DC magnetron sputtering, Rare Met. 25(6 Suppl. 1), 82 (2006)

[40] X. Xie and G. Shen , Single-crystalline In₂S₃ nanowire-based flexible visible-light photodetectors with an ultra-high photoresponse, Nanoscale 7(11), 5046 (2015)

[41] B. Zhang , C. Niu , W. Chu , X. Guo , X. Zhou , C. Li , X. Fan , L. Zou , Z. Wu , Y. Lu , F. OuYang , Y. Zhou , and H. Zhang , Synthesis of 2D nonlayered α-Nb₂O₅ nanosheets by the growth promoter of sulfur and alkali halides, Phys. Status Solidi RRL. 18(8), 2400054 (2024)

[42] W. Wu , L. Wang , R. Yu , Y. Liu , S. H. Wei , J. Hone , and Z. L. Wang , Piezophototronic effect in single‐atomic‐layer MoS₂ for strain‐gated flexible optoelectronics, Adv. Mater. 28(38), 8463 (2016)

[43] S. R. Tamalampudi , Y. Y. Lu , R. Kumar U. , R. Sankar , C. D. Liao , K. M. B , C. H. Cheng , F. C. Chou , and Y. T. Chen , High performance and bendable few-layered InSe photodetecters with broad spectral response, Nano Lett. 14(5), 2800 (2014)

[44] T. Zhu , Y. Zhang , X. Wei , M. Jiang , and H. Xu , The rise of two-dimensional tellurium for next-generation electronics and optoelectronics, Front. Phys. (Beijing) 18(3), 33601 (2023)

[45] B. Liu , W. Chu , S. Liu , Y. Zhou , L. Zou , J. Fu , M. Liu , X. Fu , F. Ouyang , and Y. Zhou , Engineering the nanostructures of solution proceed In₂Se_xS_3−x films with enhanced near-infrared absorption for photoelectrochemical water splitting, J. Phys. D 55(43), 434004 (2022)

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